Rev 215 SOST Segment Titan Rainclouds 2015-129T08:15:00-131T18:00:00 Rhea No Targeted Flybys; Highlights

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Rev 215 SOST Segment Titan rainclouds 2015-129T08:15:00-131T18:00:00 Rhea No targeted flybys; Highlights: CIRS distant observation (ISS, VIMS, UVIS in ridealong) from 129T16:45-22:20 of Tethys and Dione to understand the spatially resolved thermal inertia, “Pacman” shape, and global energy balance. Tethys large solar phase angle; Dione moderate. Tethys (above); Dione (below) ISS Plume PIE observation at 130T00:30 (06:35 duration); another plume non-PIE on day 151 (not SOST segment) ISS outer irregular rock observation at 130T22:25 CIRS PDT Design for 10+ hours. The goal is to determine the dynamical state (rotation period and pole position). Helene Rev 215 SOST Segment, cont’d. Titan rainclouds Rhea Flyby of Polydeuces BEST EVER by a factor of 2 Polydeuces is a Dione Lagrangian that was discovered by Cassini. The goal of this observation is to study its morphology, size, albedo, and derive its composition to understand its origin and relationship to Dione and other moons. Observation starts at 129T22:20 (May 10, 2015), with a closest approach around 34,000 with a moderate solar phase angle. This is just the resolution where features (craters, CIRS PDT Design etc.) may start to appear on this irregular moon. Polydeuces, Cassini’s own satellite Helene Hyperion observing campaign (Not a PIE) Rhea On rev 216-217 (XD Segment) there is a ~34,000 ORS Hyperion Flyby designed to cover regions that may have poorly imaged (Hyperion is in chaotic rotation, so the location will be a surprise). The solar phase angle is moderate throughout the observing period, which is ideal for mapping geologic Features. Tethys Composition and thermal properties will also be studied. The observations extend From 2015- CIRS PDT Design 151T09:22-19:00. ISS is prime with CIRS and UVIS in ridealong. Hyperion Helene Rev 217 Dione MAPS flyby (516 km) Segment 166T15:30-169T15:29 MAPS flyby to understand Dione environment and dust and interactions between particles and the surface; focus is on N. pole. Does Dione have a native source? C/A 2015-167T20:11:52.44 RSS is also in ridealong: This key observation will substantially improve our knowledge of Dione’s interior structure and the rigidity of its crust ISS reg map view (above) Other key observations: CIRS map view (below) Tarvos (outer moon): rotation period Rhea: CIRS inbound observation Polydeuces: clone of May 10 event ISS regional map of Dione (inbound lit) CIRS map of Dione (outbound dark) Outer moon observations Saturn UVIS PIE.

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Arxiv:1912.09192V2 [Astro-Ph.EP] 24 Feb 2020
Draft version February 25, 2020 Typeset using LATEX preprint style in AASTeX62 Photometric analyses of Saturn's small moons: Aegaeon, Methone and Pallene are dark; Helene and Calypso are bright. M. M. Hedman,1 P. Helfenstein,2 R. O. Chancia,1, 3 P. Thomas,2 E. Roussos,4 C. Paranicas,5 and A. J. Verbiscer6 1Department of Physics, University of Idaho, Moscow, ID 83844 2Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca NY 14853 3Center for Imaging Science, Rochester Institute of Technology, Rochester NY 14623 4Max Planck Institute for Solar System Research, Göttingen,Germany 37077 5APL, John Hopkins University, Laurel MD 20723 6Department of Astronomy, University of Virginia, Charlottesville, VA 22904 ABSTRACT We examine the surface brightnesses of Saturn's smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates compar- isons among different moons. Analyses of Cassini imaging data with this model reveals that the moons Aegaeon, Methone and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons' surface brightnesses being entirely controlled by the local flux of E-ring par- ticles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso's and Helene's excess brightness.
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The Orbits of Saturn's Small Satellites Derived From
The Astronomical Journal, 132:692–710, 2006 August A # 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE ORBITS OF SATURN’S SMALL SATELLITES DERIVED FROM COMBINED HISTORIC AND CASSINI IMAGING OBSERVATIONS J. N. Spitale CICLOPS, Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301; [email protected] R. A. Jacobson Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 C. C. Porco CICLOPS, Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 and W. M. Owen, Jr. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 Received 2006 February 28; accepted 2006 April 12 ABSTRACT We report on the orbits of the small, inner Saturnian satellites, either recovered or newly discovered in recent Cassini imaging observations. The orbits presented here reflect improvements over our previously published values in that the time base of Cassini observations has been extended, and numerical orbital integrations have been performed in those cases in which simple precessing elliptical, inclined orbit solutions were found to be inadequate. Using combined Cassini and Voyager observations, we obtain an eccentricity for Pan 7 times smaller than previously reported because of the predominance of higher quality Cassini data in the fit. The orbit of the small satellite (S/2005 S1 [Daphnis]) discovered by Cassini in the Keeler gap in the outer A ring appears to be circular and coplanar; no external perturbations are appar- ent. Refined orbits of Atlas, Prometheus, Pandora, Janus, and Epimetheus are based on Cassini , Voyager, Hubble Space Telescope, and Earth-based data and a numerical integration perturbed by all the massive satellites and each other.
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The Gravity Field and Interior Structure of Dione
The gravity field and interior structure of Dione Marco Zannoni1*, Douglas Hemingway2,3, Luis Gomez Casajus1, Paolo Tortora1 1Dipartimento di Ingegneria Industriale, Università di Bologna, Forlì, Italy 2Department of Earth & Planetary Science, University of California Berkeley, Berkeley, California, USA 3Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC, USA *Corresponding author. Abstract During its mission in the Saturn system, Cassini performed five close flybys of Dione. During three of them, radio tracking data were collected during the closest approach, allowing estimation of the full degree-2 gravity field by precise spacecraft orbit determination. 6 The gravity field of Dione is dominated by J2 and C22, for which our best estimates are J2 x 10 = 1496 ± 11 and 6 C22 x 10 = 364.8 ± 1.8 (unnormalized coefficients, 1-σ uncertainty). Their ratio is J2/C22 = 4.102 ± 0.044, showing a significative departure (about 17-σ) from the theoretical value of 10/3, predicted for a relaxed body in slow, synchronous rotation around a planet. Therefore, it is not possible to retrieve the moment of inertia directly from the measured gravitational field. The interior structure of Dione is investigated by a combined analysis of its gravity and topography, which exhibits an even larger deviation from hydrostatic equilibrium, suggesting some degree of compensation. The gravity of Dione is far from the expectation for an undifferentiated hydrostatic body, so we built a series of three-layer models, and considered both Airy and Pratt compensation mechanisms. The interpretation is non-unique, but Dione’s excess topography may suggest some degree of Airy-type isostasy, meaning that the outer ice shell is underlain by a higher density, lower viscosity layer, such as a subsurface liquid water ocean.
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The Sources and Dynamical Mechanisms Responsible for Differing Regolith Cover on Satellites Embedded in Saturn’S E Ring
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PDS4 Context List
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